1. Field of the invention
The invention concerns valves and in particular stream turbine control valves.
2. Description of the prior art
These valves are used to control the flowrate of the steam to the turbine; at low flowrates the valve provides a small cross-section passage for the steam and because of pressure differences between the inlet and outlet sides of the valve supersonic speeds are produced near the area in which the valve obturator or closure into contact with the valve seat. Shockwaves and separation of the fluid from the valve walls can then occur and cause the valve to vibrate and an excessive noise level.
One solution to this problem is to divide the flow into a plurality of small jets. This can be achieved with a valve seat incorporating a throttling flange with slots in its circumference separating the throttling flange into crenellations as described, for example in French utility patent No 76 12647.
A number of large steam turbines throughout the world are equipped with such valves, but it has been found that some level of vibration persists under partial load conditions.
The valve in accordance with the invention for eliminating vibration under partial load conditions is characterized in that each crenellation comprises on its surface facing the valve obturator a vertical central partition between two symmetrical openings.
The symmetrical openings can be cells or chamfers.
The partition has a width between 1/10th and 1/5th the width of the crenellation.
The present invention will be better understood from the following description.